This invention relates to the field of three dimensional (3D) computer graphics systems. More particularly, but not exclusively, this invention relates to generation of images in real time for graphics systems with limited fill-rate capabilities.
A three dimensional computer graphics system generates projections of 3D computer models on a device known as a frame buffer. In order to generate a projection of a 3D model, the system relies on software and hardware to process the 3D model and calculate the colour of each pixel in the frame buffer. In interactive real-time applications, where a user manipulates the 3D model and expects ‘instant’ reactions to his/her inputs, this processing of the entire 3D model needs to happen at least 10 times per second. If the model is displayed in an stereoscopic display, two images are required, one per eye, which results in processing speeds of 20 times per second.
In medical and scientific applications, the system needs to ensure that the original high quality and fine detail of the images (CT and/or MRI scans, for example) results in a high quality display. This requires a frame buffer that has as many resolvable pixels as possible. Frame buffer sizes of 1280×1024 are common today. The hardware that drives the frame buffer is required to calculate the colour of each of the 1,310,720 pixels 20 times per second, or 26,214,400 pixel operations per second. This fill-rate operation is one of the key limiting factors of the speed at which a 3D model can be rendered, and therefore imposes a limit on the interactivity that the user can have with the 3D model. If the entire 3D model moves (is rotated or scaled) then the entire frame buffer needs to be recomputed and updated. If the 3D model changes (its components change over time), then the frame buffer also needs complete recomputation and updating.
It is an object of the invention to provide a method of generating a 3D image which alleviates this problem of the prior art.